Lift-off is a general term for a process of forming a pattern of organic or inorganic thin layers by:
applying a resist onto a workpiece surface;
patterning the resist layer by a photolithography technique;
depositing and/or sputtering an organic or inorganic substance over the resist layer and areas in which the resist has been cleared; and
releasing the resist layer together with the overlying organic or inorganic thin layer.
As a consequence, the organic or inorganic substance found in the orifices of the resist layer remains there to form a desired pattern.
In this lift-off process, the resist pattern profile is very important. For example, positive resists will typically produce a pattern which tapers forward as shown in FIG. 2(c). Releasing of this forward tapered resist will result in a pattern of layers having burrs on their edges as shown in FIG. 2(d).
A specific example will be given with respect to the processing of MR magnetic head sliders. Here, the aforesaid lift-off process is used to form a DLC (diamond like carbon) layer on an ABS (air bearing surface) for the purpose of pad protection. As described above, the lift-off process can produce burrs on the edges of DLC layers. The burrs on the DLC layers can scratch the magnetic recording disks of HDD (hard disk drive) or can be a foreign object to cause HDD failures.
With such problems, it will be effective to use negative resists or image reversal resists which can be formed into a reverse tapered pattern. As shown in FIG. 3(c), the orifices of this reverse tapered layer have a larger size in the bottom than in the top, so that the formation of burrs can be prevented.
However, this method in general has a difficult control of the resist pattern profile. Further, it is difficult to observe the resist pattern with a light microscope and also to release the resist layer which has been hardened.
In respect to the workpiece surface as a substrate, it will usually have irregularities, which are relatively large for the thickness of applied resist, as a result of the process steps the workpiece has undergone. Because of this, it has been difficult to form a resist layer in uniform thickness.
In the above processing of MR magnetic heads, a number of strip pieces called row bars are processed as being stuck on a jog with their ABS upward. Since these row bars have a gap between the neighboring ones, a direct application of a liquid resist is impossible; therefore, a resist film such as a dry film is generally employed instead.
From the viewpoint of improving the productivity of workpieces, there has been a need for a technology which can be incorporated into the production process without disrupting the flow of process steps and by which a pattern can be readily formed on a workpiece surface.
The present inventors studied earnestly in view of the aforesaid circumstances. As a result, they have developed a two-layer laminate that comprises a resist layer (I) formed from a specific positive radiation-sensitive resin composition 1 and a resist layer (II) formed from a specific positive radiation-sensitive resin composition 2. This two-layer laminate can be formed into an undercut resist pattern by single photoexposure and development. Thus, the patterning method using the two-layer laminate can produce a burr-free layer with ease. The present invention has been completed based on these findings.
It is an object of the invention to provide a resist layer which can leave a burr-free layer on a substrate with ease, and a patterning method using the same.